middle   layer;   and   the   pia   mater   is   the   vascular inner-most layer that adheres to the surface of the brain and   spinal   cord.   Inflammation   of   the   meninges   is called  meningitis.  The  type  of  meningitis  contracted depends upon whether the brain, spinal cord, or both are affected, as well as whether it is caused by viruses, bacteria, protozoa, yeasts, or fungi. CEREBROSPINAL  FLUID.—Cerebrospinal fluid   is   formed   by   a   plexus,   or   network,   of   blood vessels in the central ventricles of the brain. It is a clear, watery  solution  similar  to  blood  plasma.  The  total quantity of spinal fluid bathing the spinal cord is about 75  ml.  This  fluid  is  constantly  being  produced  and reabsorbed. It circulates over the surface of the brain and spinal cord and serves as a protective cushion as well as a means of exchange for nutrients and waste materials. Spinal Cord The  spinal  cord  is  continuous  with  the  medulla oblongata  and  extends  from  the  foramen  magnum, through the atlas, to the lower border of the first lumbar vertebra, where it tapers to a point. The spinal cord is surrounded  by  the  bony  walls  of  the  vertebral  canal (fig.   1-44).   Ensheathed   in   the   three   protective meninges  and  surrounded  by  fatty  tissue  and  blood vessels, the cord does not completely fill the vertebral canal, nor does it extend the full length of it. The nerve roots serving the lumbar and sacral regions must pass some distance down the canal before making their exit. The  sympathetic  trunk  contains  the  paravertebral ganglia (sing. ganglion), knotlike masses of nerve cell bodies (fig. 1-44). A cross section of the spinal cord shows white and gray   matter   (fig.   1-45).   The   outer   white   matter   is composed   of   bundles   of   myelinated   nerve   fibers arranged   in   functionally   specialized   tracts.   It establishes  motor  communication  between  the  brain and   the   body   parts.   The   inner   gray   unmyelinated 1-38 HM3f0143 MOTOR AREAS INVOLVED WITH THE CONTROL OF VOLUNTARY MUSCLES CONCENTRATION, PLANNING, PROBLEM SOLVING FRONTAL LOBE MOTOR SPEECH AREA (BROCA'S  AREA) INTERPRETATION OF SENSORY EXPERIENCES, MEMORY OF VISUAL  AND AUDITORY PATTERNS TEMPORAL LOBE BRAIN STEM VISUAL AREA VISUAL IMAGES, VISUAL RECOGNITION OF OBJECTS OCCIPITAL LOBE GENERAL INTERPRETATIVE AREA PARIETAL LOBE UNDERSTANDING SPEECH, USING WORDS SENSORY AREA INVOLVED WITH CUTANEOUS AND OTHER SENSES CEREBELLUM AUDITORY AREA Figure 1-43.—Functional areas of the brain. HM3F0144 SYMPATHETIC TRUNK PARAVERTEBRAL GANGLION SPINE NERVES TRANSVERSE PROCESS INTERVERTEBRAL FORAMEN POSTERIOR ROOT DORSAL ROOT GANGLION PIA MATER ARACHNOID MATER DURA MATER VERTEBRAL CANAL BODY OF VERTEBRA ANTERIOR ROOT SPINAL CORD Figure 1-44.—Spinal cord.